Nutritional studies have indicated that some of the essential amino acid threonine in various plant proteins including soybean, peanut and wheat gluten is biologically unavailable. This becomes a nutritional problem for people subsisting on marginal diets deficient in protein or composed primarily of plant protein. The reason for the poor availability of threonine is not clear. Little is known about the structure of most of these plant proteins other than their amino acid content. This research is designed to elucidate those structural features of soybean proteins which could influence the availability of threonine by preventing its release by digestive enzymes. The structural studies are directed to identification of the bonding and amino acid sequence in the vicinity of threonine. The research procedure will involve a study of the rate and extent of release of free threonine during proteolysis with Pronase and with digestive enzymes. Threonine-containing peptides which tend to accumulate during proteolysis will be isolated and identified.